In the first type of known tabulation systems, the various positions of arrest of the carriage are defined by a series of stop pins or studs located on the usual tabulator bar and settable selectively by the operator to define the positions of arrest.
In these systems, the travel of the carriage is controlled by the stop at which the carriage has halted, the said stop selecting a group of stops for the following stopping of the carriage. The tabulation effected in this way is excessively rigid and complicated, owing to the fact that after the first stop of the carriage it is no longer possible to alter the following stops.
In a second type of tabulation system, there is prearranged a first store comprising cams which indicates from time to time the actual position of the carriage according to the combination of teeth and hollows of the cams themselves, and a second store which can be set by programme is constituted by a series of mechanical elements having two positions, the combination of which represents the tabulation position to be reached. For effecting comparison of the contents of the said two stores there is prearranged a first series of sensing elements which sense the said cams and the said two-position elements simultaneously in order to control command means to shift the carriage when the contents of the two stores are not equal. A second series of sensing elements is moreover provided for arresting the carriage which are controlled by the first series of sensing elements when the first store indicates a position of the carriage equal to that of the second store.
This tabulation system has two fundamental disadvantages: the first consists of the fact that it is very complex in construction inasmuch as it comprises two stores and two series of sensing elements, one for controlling the travel of the carriage and the other for controlling the stopping thereof.
The second disadvantage, which is directly consequent, is that all the aforesaid mechanisms move sequentially, as a result of which the duration of a tabulation cycle is extremely long.